The present invention relates to a power supplier, and more particularly to an improved type of power supplier for a magnetron employed in electric appliances, such as a microwave oven.
In a magnetron, it is known that the current voltage characteristic is non-linear. More particularly, the voltage, in the initial stage, increases rapidly up to a certain level, namely a threshold voltage, with a slight increase of the current. Then, in the second stage, i.e., after the voltage reaches the threshold voltage, only a slight further increase of voltage occurs in relation to a considerable increase in the current. It is in the second stage that the magnetron is operated to produce the microwaves. In operating the magnetron, even trivial change or fluctuation in the voltage applied to the magnetron may cause an extreme change in the current, thus causing undesirable fluctuations in the output power. Therefore, in the conventional power supplier for the magnetron, the type of transformer employed therein is a so called constant-current transformer for stabilizing the output power of the magnetron. Such a constant-current transformer is designed to effect voltage regulation by means of a saturated core resonant circuit structure having an inductance portion constituted by a leakage transformer for voltage step-up, and a capacitance portion connected to the secondary side of the transformer.
Such type of transformer requires a comparatively large size core which makes the power supplier large in size and heavy.
Furthermore, in the conventional power supplier, the input power to be applied to the magnetron is controlled in the transformer in which the secondary winding is provided with a plurality of tabs each connected to the secondary winding at particular turns of the winding. The input power can be changed by a change of the tab connected to the magnetron. Such a change in the connection can not be easily carried out because the current flowing therethrough is comparatively large.